I think this one is hard to reproduce because I only see it every now and then
and I can't even seem to reproduce it now, however it happens quite often.

Open one browser window and go to a web page, like http://planet.gnome.org/
Go to another workspace and open a new web browser window and go to a web page
that has a form.
Sometimes you cannot enter text into the form, the cursor focus will be in the
text entry area, but nothing you type gets in there.

This happened today and by luck I went back to the other window in the other
worspace to close it and restart ephy (which is what I usually do when this
happens).  But I saw that the other ephy window had done a 'type-ahead find' for
the text I was trying to enter into the form on the other window.  I had to
close the other window in order to get the proper focus back to the window with
the form.

Hope that helps!